Passive Balancing, 4 cells

by VladM

20 parts

Four cells in series start at 3.0, 3.2, 3.3 and 3.4V. Each has a 33Ω bleed resistor behind a switch driven by a balance bit, the way a battery-management chip enables balancing cell by cell. Press Run, then press bit4 (it reads 1): the 3.4V cell bleeds through Rbal4 and its voltage falls. Press bit4 again when it reaches the cell you are balancing to — about 2 seconds on screen to 3.3V, 8 seconds to 3.0V (24 and 103ms of the circuit's own time). The other bits do the same for their cells. The switch symbols do not move; the bit's 0/1 and the I probe show when a bleeder conducts. Real pack: 33Ω on a 3.3V cell bleeds about 100mA; a 100Ah cell would take about 10 hours per 1% of state of charge, which is why passive balancing works slowly, mostly near the top of charge.